(Beyond Pesticides, May 3, 2010) Researchers have found that silver nanoparticles can migrate out of fabrics that have been treated with the particles for its antibacterial properties when it is exposed to simulated perspiration, raising concerns about human exposure to nanosilver through skin absorption. This is the first study to use artificial sweat to mimic the conditions of human skin, however it is not clear if the silver materials in sweat would be absorbed through human skin.

Silver has long been used as an antiseptic to reduce bacterial growth on skin, however recent advances in nanoscience (the science and manipulation of chemical and biological materials with dimensions in the range from 1-100 nanometers) led to the development of silver nanoparticles. Due to their small size, these nanoparticles are able to invade bacteria and other microorganisms and kill them, and silver nanoparticles (or nanosilver) are now widely impregnated into a wide range of consumer products, including textiles such as socks, sportswear, underwear and bedding, vacuums, washing machines, toys, sunscreens, and a host of others.

The researchers tested and compared eleven different fabrics for the study, â€śDetermination of silver nanoparticle release from antibacterial fabrics into artificial sweatâ€ť in Particle and Fibre Toxicology journal. Six of the fabrics were commercially made shirts that were sold as containing nanosilver, and five fabrics were treated in the lab with a silver nanoparticle solution containing nanoparticles of silver chloride and titanium dioxide. The lab-prepared fabrics were treated with 0, 0.5, 1, 5 and 10 grams per liter of the nanosilver solution. The fabric was then incubated for 24 hours in four formulations of artificial sweat varying in acidity but containing the same compounds as human sweat (i.e. lactic acid, salt compounds, water). After the fabric was removed, the artificial sweat was analyzed for silver nanoparticles. Researchers then compared which fabrics were effective at reducing bacterial growth for Staphylococcus aureaus (staph) and E. coli by incubating the bacteria with the fabric samples and counting the results.

Silver content in the lab prepared fabrics ranged from 36 to 425 milligrams of silver per kilogram (mg/kg), and released up to 322 mg/kg of fabric weight of the silver nanoparticles. The consumer fabrics, on the other hand, contained less silver to begin with, between 1 and 15 mg/kg, therefore releasing less silver into the artificial sweat. Researchers also found that half of the commercially made shirts did not contain any silver or feature any antibacterial properties, despite being labeled so. Overall, the lab-prepared fabrics released more silver nanoparticles into the artificial sweat and were more able to reduce bacterial growth than the store-bought ones, with the exception of one that inhibited bacterial growth similarly to that of the lab-prepared shirts while leaching less nanoparticles (0.5 mg/kg).

The researchers conclude that as nanotechnology becomes increasingly prevalent in consumer products, the potential for exposure to nanoparticles increases. Yet, little is known about how these silver materials may interact with people’s bodies. There is concern that the the tiny particles may be more toxic than other, larger-sized and more traditional types of silver compounds, as the smaller particles could be more easily absorbed and distributed throughout the body.

The authors suggest more research is needed to better understand the risks associated with nanotechnologies as more consumer products, such as socks and other clothing fabrics, incorporate silver nanoparticles in an attempt to reduce bacterial growth and the odors associated with it. Other studies have reported that silver can migrate from treated fabrics during washing in a washing machine. The silver from these particles are presumed to be carried into the environment by wastewater, causing concerns for aquatic life.

The study highlights a potential exposure source of nanoparticles that we know very little about in terms of the potential health effects. More research is needed to better understand the risks associated with nanotechnologies as more consumer products, such as socks and other clothing fabrics, incorporate silver nanoparticles in an attempt to reduce bacterial growth and the odors associated with it.

Current regulations fail to guarantee consumers that these new technologies are safe to use. All pesticidal substances must be registered with the U.S. Environmental Protection Agency (EPA) in accordance with the Federal Insecticide Fungicide and Rodenticide Act (FIFRA). Under FIFRA, silver nanoparticles meet the definition of a pesticide- that is, as a substance that is intended to disinfect, sanitize, reduce, or mitigate growth or development of microbiological organisms. As such, silver nanoparticles, with their antimicrobial activity, should and must be regulated by the EPA as a pesticide. However EPA has done little to regulate or evaluate the potential health and environmental impacts these particles may cause. In 2008, the International Center for Technology Assessment (ICTA), and a coalition of consumer, health, and environmental groups, including Beyond Pesticides, filed a petition with the EPA challenging the agencyâ€™s failure to regulate nanomaterials.

With an increasing number of scientific studies looking at these antibacterial substances, two basic, yet important, questions arise: Are they safe for human health and the environment? And are they necessary?

For more information, including tips on how to get toxic antimicrobials out of your home, school, office or community, visit Beyond Pesticidesâ€™ Antibacterials program page.

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